Isomerization of n-paraffin hydrocarbons



United States Patent ISOMERIZATION OF N-PARAFFIN HYDROCARBONS Norman L.Carr, Crystal Lake, 111., assignor to The Pure Oil Company, Chicago,Ill., a corporation of Ohio No Drawing. Application October 31, 1956Serial No. 619,404

10 Claims. ((31:260-683-66) This invention relates to the isomerizationof saturated, aliphatic and alicyclic hydrocarbons or mixtures thereof.It is more directly concerned with an isomerization process in which isemployed a solid catalyst for promoting the efficiency of theisomerization reaction.

A considerable onus is placed on petroleum refiners because of theincreasing octane requirements of modern, high-speed, high-compression,internal combustion engines, and the competitive market to providesuitable gasoline motor fuels for use in these engines. In formulating agasoline motor fuel, a major portion of the composition consists ofgasolines derived from the catalytic cracking of petroleum gas oilfractions. The remainder of the composition can be from light virgindistillates employed without further treating; however, it is desirableto upgrade these light distillate naphthas to produce higher octaneblending stocks. To effect this end, a variety of refining processessuch as reforming, isomerization, alkylation, or polymerization can beused with attendant advantages. Isomerization of suitable feed stocksproduces high-octane-number, branch-chain parafiins which can beincorporated in gasoline blends to promote a more eflicient utilizationof tetraethyl lead. Isomerized parafiinic blending stocks are desirablebecause of their very low sensitivity. Sensitivity is a critetion of agasolines ability to perform under road conditions, and is thedifference between the research octane number (CRC Designation F-1-545)and the motor octane number (CRC Designation F2-545). The sensitivity ofseveral gasolines is shown in Table I:

TABLE I Octane values of representative blending stocks 1 Containing 3cc. of tetraethyl lead/gallon.

refractory, metal oxide catalyst which can be employed for extendedperiods without regeneration. A further object of this invention is toprovide a promoted, refractory metal oxide, isomerization catalyst whichis susceptible to regeneration for re-use. An additional object of thisinvention is to provide an isomerization process for upgrading lightpetroleum naphthas predominantly containing C -C saturated hydrocarbonsto produce high-octane-number blending agents for use in the formulationof high-grade, gasoline motor fuels.

In copending application, entitled Isomerization Catalyst and Process,Serial No. 619,376, filed October 31, 1956, by Norman L. Carr there isdescribed a composite isomerization catalyst of increased stability andhigh activity which comprises a refractory, mixed-oxides base compositedto evince acidic properties and hydrocarbon cracking activity, e.g.,silica-alumina, having incorporated therein a hydrogenation agent suchas metallic nickel. According to the invention described therein, it hasbeen found that in order to provide a catalyst of maximum efliciency, itis necessary to condition the composite catalyst prior to use by meansof a plural-step preconditioning process employing a sequentialoxidation and hydrogenation treatment. Essentially, the conditioningprocess which has been found to be uniquely elfective can be dividedinto two parts; namely, (A) the catalyst preparation carried outsubstantially in accordance with the prior art, and (B) thepreconditioning steps which have been found to be exceptionally anddistinctively efiective for inducing high activity and stability byimparting resistance to permanent depreciation in activity. In thepre-conditioning phase of the invention described in the copendingapplication, the silica-alumina hydrogenation agent composite, afterbeing prepared and activated substantially in accordance with theteachings in the prior art, is further subjected to an oxidizingatmosphere maintained at a temperature of 650750 F. Following thisoxidation, the oxidized catalyst is contacted with'hydrogen at the sametemperature as that at which the oxidation was carried out to reduce thecomponents of the composition to their most reducible stage at thesereduction conditions and produce a composite catalyst of high activitywhich is resistant to degeneration. Included among the catalystcompositions which were prepared in accordance with the inventiondescribed in the copending application are metallic-nickel-containingcomposites. It has now been found that the eifectiveness ofmetallic-nickel-containing catalysts of this type can be furtherenhanced by incorporating molybdena in the catalyst composition.According to this invention, superior catalysts which are rela-' tivelysulphur resistant, have exceptionallyv long active lives, and havesuperior activities and selectivities, are

provided by incorporating small amounts of molybdena in the compositionconsisting of nickel supported on a refractory, mixed oxidesbasecomposited to evince acidic properties and hydrocarbon crackingactivity. In em:

Another advantage in the use of isomerization processes for upgradinggasoline blending stocks is the excellent octane-yield relationshipwhich permits the production of high-octane-number hydrocarbon fractionsor light naphtha distillates without incurring concomitant losses inyields due to the formation of undesirable byproducts.

Although extensive work has been done in investigating the isomerizationof parailinic hydrocarbons employing anhydrous aluminum chloridecatalysts in a liquid-phase process, the use of solid catalysts forpromoting this reaction in vapor phase has become important because ofthe advantages which accrue in their use. It is therefore an object ofthis invention to provide a solid catalyst having high-activity andselectivity for-the isomerization of saturated; aliphatic and alicyclichydrocarbons. Another object of this invention is to provide apromoted,-

ploying these catalysts in a vapor-phase isomerization process, thetreatment of saturated aliphaticand/or alicyclic-hydrocarbon-containingfeed stocks is carried out under the following conditions:

Temperature, F.- 600-700 Pressure, p.s.i.g. 1000 Liquid volume hourly.space velocity 0.1-2.0 Hydrogen/hydrocarbon mol ratio 0.5-4.5

In preparing the supported nickel-molybdena catalysts employed in thisinvention, conventional catalyst pre'paration techniques can be employedsuch as those discussed in Catalysis I, Emmett, Reinhold, 1954, at page315, et seq. Althoughprecipitation and gel formation can be employedfor-specific catalyst preparations-,"th'e' simplest'an'd preferredmethod of producingthe supported Patented Dec. 15, 19.59

of this invention involves the technique of impregnating the refractory,mixed oxides used as supports, with nickel and molybdena. In this methodof preparation, the required quantity of. a powdered or granular,refractory, mixed oxides support is admixed with an aqueous solutioncontaining the promoting constituents which are then precipitated intotthe pores of the support. After filtering and drying, the catalyst isagglomerated into pellets of suitable size and subsequently activated byheating the catalyst to an elevated temperature in a stream of hydrogenfor a time sufficient to elfect the reduction of the reducibleconstituents to their maximum state of reduction under the conditions ofthe activation. It is to 'be understood that the preparation andactivation of the catalyst is to be supplemented by subjecting thecatalyst activated in this manner to the pre-conditioning techniquedescribed in the co pending application cited supra. Additional methodsfor preparing a supported nickel-molybdena catalyst for pelleting andactivation include, but are not limited to, the following catalystpreparation techniques.

A suitable refractory, mixed oxides base is impregnated by immersion inan aqueous, solution of a decomposable molybdenum salt, such asammoniacal ammonium paramolybdate. The impregnated carrier is dried andheated to temperatures sufficient to decompose the molybdenum salt tomolybdic oxide, M The support, impregnated with molybdic oxide, isthereafter slurried in an aqueous solution of a decomposable nickelsalt, such as nickel nitrate. After drying, the resulting mass,impregnated with decomposable nickel salt, is heated to an elevatedtemperature sufficient to decompose the nickel salt to form nickeloxide. This two-step impregnation process can alternatively be carriedout by first introducing into the refractory, mixed oxides support thenickel salt, and thereafter following an appropriate sequentialtreatment to introduce the molybdic oxide into the catalyst composition.

The incorporation of the nickel and molybdena promoting agents in themixed oxides support can also be carried out employing co-p'recipitationtechniques which involve the precipitation of a decomposable nickelcompound from an aqueous solution of a nickel salt, such as nickelnitrate or nickel sulfate, by the addition of an aqueous solution ofammonium molybdate. This preparation can be carried out on a suitable,mixed oxides carrier by first impregnating the carrier with either thenickel or molybdenum salt, and thereafter contacting thethus-impregnated carrier with the other salt. However, an aqueousimpregnation solution, preferably containing a slight excess of ammonia,can be prepared by dissolving a water-soluble salt of nickel and awater-soluble molybdenum salt in an aqueous ammoniacal solution. Thecarrier is then immersed in the impreg'nationsolution, which is adsorbedthereon. The impregnated silicacontaining carrier is then dried andcalcined to decompose the adsorbed metal compounds. In anothersugnickel-molybdena catalyst going catalyst preparations employ acarrier in finished form as the support, it is to be understood that theprecipitation of the nickel and molybdenum promoters can be effected oncarriers in the undried, hydrous gel form. Although a variety ofcatalyst preparation methods can be employed, the manipulative stepsmust be such that unconditioned, virgin catalyst, which is thereafterpreconditioned in accordance with this invention, will comprise nickeland molybdena supported on a refractory, mixed oxides base composited toevince acidic properties and hydrocarbon cracking acivity, in which thenickel is present substantially in the metallic state and the molybdenais present in the lowest oxide form. Accordingly, in the preparation ofthe unconditioned, virgin catalyst, elevated temperatures which bringabout the complete reduction of the molybdena to the metallic state areto be avoided. Thereafter, the virgin catalyst is preconditioned inaccordance with the technique described above.

As a specific example, a nickcl-rnolybdena-silicaalumina catalystemployed in the isomerization process of this invention was prepared asfollows: An ammoniacal solution of para-molybdate was prepared bydissolving 32 grams of ammonium heptamolybdate gested technique forincorporating the molybdenum constituent in the cracking catalystcarrier, the carrier is impregnated with an aqueous solution ofmolybdenum pentachloride, and, upon drying and calcining the impregnatedbase, molybdenum trioxide is formed. Thereafter, the nickel constituentmay be incorporated in any suitable manner, such as the above-describedtwo-stage impregnation technique. See also various techniques suggestedin US. Patent 2,739,133 for combining molybdena with the selectedcarrier. The amounts of nickel and molybdenum salts employed aredependent uponthe respective amounts of nickel and molybdenum desired inthe finished catalyst as will hereinafter be considered. The preferredquantities are the stoichiometric amounts necessary to formtheoretically nickel molybdate. -Because the amounts of nickel andmolybdenum in the final composition vary within a preferred range,

other concentrations can be used. Although the forein 270 ml. ofdistilled water to a salt content of about 11% by weight. To thissolution was added 20 cc. of concentrated ammonium hydroxide to providean NH OH/ H O ratio of about 0.075/1. An 18 weight percent solution ofnickel nitrate was prepared by dissolving 58.7 grams of Ni(NO .6H O in270 ml. of water, and the molybdenumand nickel-containing solutions wereseparatelyheated to about 176 F. and admixed. To this mixture was added360 grams of silica-alumina, sufiicient to yield a finished catalystcontaining 10% of nickel molybdate. The composition of the commerciallyprepared silica-alumina 1 was:

Component: Wt. percent A1 0 23.12 Na O 0.02 Fe 0.02 80., 0.25 SiO- 76.59

1 0 8: G3,, October 17, 1955, at page 121 et seq.

The resulting slurry was mixed for one hour at 176 F., and then wasfiltered, washed with water, and dried for 16 hours in an oven at 230 F.to provide a green composite containing 10% NiMoO on the silica-aluminasupport. To initially activate the catalyst, 167 grams of green catalystwas inserted in a reactor and heated rapidly to 400 F. with 10 s.c.f.h.hydrogen flowing through the reactor. The temperature of the catalystwas raised, at a rate of F. per hour, to 975 F. employing a hydrogenrate of 10 s.c.f.h. This hydrogen rate and temperature was maintainedfor one hour after which the hydrogen rate was reduced to 4 s.c.f.h. andheld for 18 hours at 975 F., i.e., until no ammonia was detected in theoff gas. The catalyst was then cooled to 800 F. with the same hydrogenrate, and purged with nitrogen to remove the hydrogen from the reactor.Following the initial activation the catalyst was pre-conditioned inaccordance with the technique described in the copending application,cited supra. In this instance the catalyst was oxidized with dry airflowing at a rate of 3 s.c.f.h. until the hot zone passed through thereactor. The oxidized catalyst was purged with nitrogen and reduced withhydrogen for 20 minutes at a rate of 10 c.f.h./ 200 ml. of catalyst at775-800 F. To initiate the onstream period, the reactor pressure wasincreased to 350 .p.s.i.g. and the catalyst cooled to 620-630" F. Basedon total composition, the finished catalyst contained 2.7% by weight ofnickel and 4.4% of molybdenumpresent as M00 supported on asilica-alumina carrier having a nominal silica/alumina concentrationratio of 75/25 based only on the carrier composition. Othernickelmolybdena-silica-alumina catalysts were similarly prepared using acarrier having a nominal silica-alumina concentration ratio of 50/50based only on carrier composition. To demonstrate the effectiveness ofthe catalyst compositions of this invention, the comparative data shownin Table II were obtained in which the superiority of preconditionednickel-molybdena-containing catalysts over preconditionednickel-containing-catalysts preconditioned in the same manner is shown.

TABLE II Liquid 1 Degener- Preconditloned Catalyst Composition RecoveryActivity ation 8 (wt. per- Rating Time, cent) hours Ni (2.7 wt.percent), M (4.4 wt. percent), 75/25 Silica/alumina 96 70 4 210+ Ni (2.7wt. percent), M0 (4.4 wt

cent), 75/25 Silica/alumina-.. 96 65 400 (2.7 wt. percent), M0 (4.4cent), 50/50 Silica/alumina... 97 66. 5 4 550+ Ni (5 wt. percent) 75/25Silica/alumina. 93 75 55 Ni (5 wt. percent), 75/25 Silica/alumina. 9373. 2 40 Ni (5 wt. percent), Kicselguhr wt.

percent) with 90% 75/25 Silica] alumina support 93 70 4 1 The conditionsunder which the liquid recoveries and activity ratings listed wereobtained were as follows: Pressure 350 p.s.i.g.; temperature about 660F.: Ji /hydrocarbon mole ratio 3.5; and liquid volume hourly spacevelocity-1.0 v./v./hr.; charge characteristics:

Component:

n-Pentanc .volume percent. 27. 9 n-Hexane do. 26. 5 n-Heptane" .do 25 6Cyelohexanedo 20.0 Gravity, API. 75.0-75.9 R1. (Na 1. 3840-16830Research Octane Number (CRO Designation 2 Activitymiih''is'iifidlfifi'isiifdfifi'iumber (on o Designation Fl-545) of theliquid product obtained from an isomerization process operated under theforegoing operating conditions and employing Aromatics, vol. percent- 2ASTM test:

LB. P 90 b The run was discontinued at this timcphoweve'r, the researchoctane of the isomerate had not yet decreased to below 76. The catalystsupport here, labeled 50/50, was a nominal 50% alumina and was composedof 35% H-4l alumina and 65% 75/25 silica/alumina in admixture. FromTable II it is seen that by incorporating small amounts of molybdena ina nickel-promoted, silica-containing catalyst there is attained anextended catalyst life without depreciation in activity or selectivityof the catalyst. Catalysts of this nature have commercial importancebecause processes in which they are used can be operated for extendedperiods of time without shutting the process down for catalystregeneration.

It also has been found that the objectives of this invention are bestachieved if the catalysts employed in the subject isomerization processhave the compositions within the following ranges:

1 Based on total catalyst composition.

The nickel and molybdena are incorporated in a refractory, mixed oxidesbase composited to evince acidic properties and hydrocarbon crackingactivity. Because isomerization reactions are acid catalyzed, a varietyof acidic mixed-oxide bases can be employed including, but not t0SIO2A1203, SIOFZIOZ, SiO2TiO2, SIO2B203, A1203-ZI'O2, Al O BeOAl O -B OSiO2 CI'O, B203 TiO2, SiO2A1203-ZI'O2, Al O --BeO, acid-treated clays,etc. The mixed oxides used in forming the base can be either in chemicalor physical combination.

To demonstrate the advantages obtained in employing compositionscontaining nickel and molybdena within the preferred concentrationranges listed above, an investigation of variousnickel-mo]ybdena-silica-alumina catalysts was carried out. In thisevaluation, the following operating conditions were used:

The synthetic-naphtha feed stock processed under these conditions hadthe same characteristics as that described in Table II above. Run dataobtained using various catalyst compositions are presented in Table IV.

TABLE IV Liquid Activity Ni 1 Mo 1 SIOg/A1g03 2 Recovery, Rating v.percent 1 Based on total catalyst composition.

2 Based only on carrier composition.

Hydrocracking was the main reaction. Hot zones caused operationalditficulties and liquid recoveries were very low at high conversionconditions. The results show that low levels of nickel (3%) andmolybdenum (1%) produce the best octane-yield when the metals arecombined on the 75/25 silica/alumina support, employed at or near highconversions and high selectivity. The results also clearly define thehigh activity and low selectivity of the catalysts comprising the 50/50silica/alumina. In employing catalysts containing less than thepreferred concentration ranges of nickel and molybdena, it was foundthat, although these catalysts had a high initial activity rating, theactivity diminished more rapidly than the preferred compositions, aresult experienced employing a 1.5Ni----1.2Mo(as MoO )75/25silica-alumina catalyst.

According to this invention, it has been shown that isomerizationcatalysts comprising nickel-molybdena supported on refractory, mixedoxides bases composited to evince acidic properties and hydrocarboncracking activity, in which the respective constituents are preferablypresent in the amounts defined herein, and when activated andpreconditioned in accordance with the technique described in copendingapplication, cited supra, provide excellent catalysts for use in theisomerization of hydrocarbons. These catalysts have long active lives,are resistant to sulfur degeneration, and possess other importantcatalyst properties. These catalysts are employed under the followingisomerization conditions:

Space velocity, 1v./hr./v. 0.1 to about 2.0, with 0.3

to 1.2 preferred. Hydrogen/hydrocarbon mole 0.5 to 4.5, with 0.5 to 3.5

ratio. preferred.

The feed stocks which can be isomerized include saturated aliphatic andalicyclic hydrocarbons having 4 to 8 carbon -7 atoms per molecule,and/or mixtures thereof. The process is especially adaptable for theupgrading of light petroleum distillates having a boiling range of about90 to 200 F., and the pentane through heptane traction of naturalgasoline.

Although the foregoing invention is specifically illustrated, there aremodifications in the various phases of this invention which will beobvious to those skilled in the art. It is well to note in this regardthat in the initial preparation of the catalyst as well-as in thepreconditioning phase it is preferred that successive steps of oxidationand reduction not be carried out without employing an intermediate purgestep to avoid the deleterious etfect on the catalyst due to the presenceof water vapor or the possibility of forming explosive mixtures ofoxygen and hydrogen. This purging, which can be carried out by using aninert gas, evacuation of the process vessel, or both, ordinarily isconventional practice which does not infiuence'the characteristics ofthe catalyst. Accordingly this invention is limited only in the mannerset forth in the following claims. This application is a continuation inpart of the copending application of Norman L. Carr, Serial No. 551,854, filed December 8, 1955, now abandoned.

What is claimed is:

1. A method of preparing a highly active, reactivatable, virginisomerization catalyst which comprises incorporating in an acidic,mixed-oxides hydrocarbon cracking catalyst support about 0.5-3.0 wt.percent of nickel in the form of a nickel compound and 1.0-5.0 wt.

percent of molybdenum as a molybdenum compound which is decomposable tomolybdenum oxide, heating the catalyst to a temperature above about 900F. and circulating a reducing gas thereover, thereby producing acatalyst composition containing nickel in substantially the metallicstate and molybdenum oxide in the most reduced form of the oxide,subjecting the reduced virgin catalyst to an oxidizing atmosphere at atemperature of about 650 to 850 F., for a time sufiicient to oxidizecompletely the oxidizable constituents of the catalyst composition, andthereafter contacting the oxidized catalyst composition withsubstantially pure hydrogen, substantially free of O and CO, at 650-800F. for a time sufficient to substantially completely reduce thereducible components of the oxidized catalyst to the lowest valencestate under the stated conditions.

2. A'method in accordance with claim 1 in which the catalyst support isarefractory acidic composite of silica and at least one refractory oxideof the group consisting of alumina, zirconia, titania, beryllia,chromia, and boria.

3. A method in accordance with claim 1 in which the catalyst support isan acidic silica-alumina composite containing 50-90% wt. silica and50-10% wt. alumina.

4. A method in accordance with claim 1 in which the catalyst supportconsists of silica-alumina containing about 75% wt. silica and wt.alumina and the resulting catalyst contains about 3% wt. nickel and 1%wt. molybdenum.

5. A method in accordance with claim 1 in which the catalyst supportconsists of silica-alumina containing about wt. silica and 25 wt.alumina and the resulting catalyst contains about 2.7% wt. nickel and4.4% wt. molybdenum.

6. A process for isomerizing a charge stock consisting essentially ofn-parafiin hydrocarbons containing 4 to 8 carbon atoms per molecule inadmixture with hydrogen at a hydrogeu/ hydrocarbon mol ratio of about0.5 to 4.5, a liquid hourly space velocity of about 0.1 to 2.0, apressure of -1000 p.s.i.g., and a temperature of 600- 700 F., by contactwith a catalyst produced and activated in accordance with the processdefined in claim 1.

7. A process for isomerizing a charge stock consisting essentially ofn-parafiin hydrocarbons containing 4 to 8 carbon atoms per molecule inadmixture with hydrogen at a hydrogen/hydrocarbon mol ratio of about 0.5to 4.5, a liquid hourly space velocity of about 0.1 to 2.0, a pressureof 150-1000 p.s.i.g., and a temperature of 600- 700 F., by contact witha catalyst produced and activated in accordance with the process definedin claim 2.

8. A process for isomerizing a charge stock consisting essentially ofn-parafiin hydrocarbons containing 4 to 8 carbon atoms per molecule inadmixture with hydrogen at a hydrogen/hydrocarbon mol ratio of about 0.5to 4.5, a liquid hourly space velocity of about 0.1 to 2.0, a pressureof 150-1000 p.s.i.g., and a temperature of 600- 700" F., by contact witha catalyst produced and activated in accordance with the process definedin claim 3.

9. A process for isomerizing a charge stock consisting essentially ofn-paraflin hydrocarbons containing 4 to 8 carbon atoms per molecule inadmixture with hydrogen at a hydrogen/hydrocarbon mol ratio of about 0.5to 4.5, a liquid hourly space velocity of about 0.1 to 2.0, a pressureof 150-1000 p.s.i.g., and a temperature of 600- 700 F., by contact witha catalyst produced and activated in accordance with the process definedin claim 4.

10. A process for isomerizing a charge stock consisting essentially ofn-paraffin hydrocarbons containing 4 to 8 carbon atoms per molecule inadmixture with hydrogen at a hydrogen/ hydrocarbon mol ratio of about0.5 to 4.5, a liquid hourly space velocity of about 0.1 to 2.0, apressure of 150-1000 p.s.i.g., and a temperature of 600- 700 F., bycontact with a catalyst produced and activated in accordance with theprocess defined in claim 5.

References Cited in the file of this patent UNITED STATES PATENTS2,687,370 Henricks Aug. 24, 1954 2,718,535 'McKinley et al Sept. 20,1955 FOREIGN PATENTS 487,392 Canada Oct. 21, 1952

1. A METHOD OF PREPARING A HIGHLY ACTIVE, REACTIVATABLE, VIRGINISOMERIZATION CATALYST WHICH COMPRISES INCORPORATING IN AN ACIDIC,MIXED-OXIDES HYDROCARBON CRACKING CATALYST SUPPORT ABOUT 0.5-3.0 WT.PERCENT OF NICKEL IN THE FORM OF A NICKEL COMPOUND AND 1.0-5.0 WT.PERCENT OF MOLYBDENUM AS A MOLYBDENUM COMPOUND WHICH IS DECOMPOSABLE TOMOLYBDENUM OXIDE, HEATING THE CATALYST TO A TEMPERATURE ABOVE ABOUT900*F. AND CIRCULATING A REDUCING GAS THEREOVER, THEREBY PRODUCING ACATALYST COMPOSITION CONTAINING NICKEL IN SUBSTANTIALLY THE METALLICSTATE AND MOLYBDENUM OXIDE IN THE MOST REDUCED FORM OF THE OXIDE,SUBJECTING THE REDUCED VIRGIN CATALYST TO AN OXIDIZING ATMOSPHERE AT ATEMPERATURE OF ABOUT 650* TO 850*F., FOR A TIME SUFFICIENT TO OXIDIZECOMPLETELY THE OXIDIZABLE CONSTITUENTS OF THE CATALYST COMPOSITION, ANDTHEREAFTER CONTACTING THE OXIDIZED CATALYST COMPOSITION WITHSUBSTANTIALLY PURE HYDROGEN, SUBSTANTIALLY FREE OF O2 AND CO, AT650*-800*F. FOR A TIME SUFFICIENT TO SUBSTANTIALLY COMPLETELY REDUCE THEREDUCIBLE COMPONENTS OF THE OXIDIZED CATALYST TO THE LOWEST VALENCESTATE UNDER THE STATED CONDITIONS.